EFFECT OF A MU-SELECTIVE OPIOID ANTAGONIST ON CCK-8-INDUCED CHANGES IN THERMOREGULATION IN THE RAT

We examined the effects of ICV injection of CCK-8 alone and in combina tion with CTAP, a mu-selective antagonist, on brain surface temperatur e (Tb), oxygen consumption (VO2), and heat exchange (Q) in unrestraine d male S-D rats at an ambient temperature of 20 +/- 0.5 degrees C. CCK -8 (300 ng, ICV) produced hyperthermia (Delta Tb: 0.86 +/- 0.22 degree s C) lasting for 30-60 min, which was associated with an increase in V O2 (1.42 +/- 0.28 ml/g/h). There was an increase in Q (1.87 +/- 1.2 ca l/g/h) beginning 15 min after injection and lasting for 60 min. The CC K-8-induced hyperthermia was attenuated by a postinjection increase in Q. During the 60-120 min postinjection period, VO2 and Q returned to baseline followed by the return of Tb to preinjection levels. CCK-8-in duced increases in Tb, Q, and VO2 were blocked by pretreatment with CT AP (0.75 mmol, ICV) 15 min earlier. CTAP alone did not significantly a ffect Delta Tb, Delta VO2, and Delta Q. These results suggest that, wi thin the thermoneutral zone, the thermoregulatory effects of CCK-8 in the rat involve participation of mu-opioid receptors. (C) 1998 Elsevie r Science Inc.